A fix that works for me was to uninstall all video drivers, install again and only install Intel Graphic Command Center from the Microsoft store. DON'T INSTALL DELL PREMIER COLOR APP that causes all the problems with black and contrast!
Sorry for my dissapearing guys but i was so bussy those weeks.
I have read all the posts, those days i also update my bios and all the BIOS without any luck.
But i have some things to mention.
A friend of mine bought a dell xps 9550 with 4k display from a guy that calibrates the colors with the Display CAL and spyder X.
I tryed the same steps that he said and it works 50%
The colors in Adobe programs and in Chrome seems accurate (not 100% but muuuch better than before) but in all the other apps, preview programs even in the background of windows everything is oversaturated!!!
Guys for you that you said that the problem solved, is not solved because you dont see the banding. The problem now is the non accurate colors!!!
What is my final thoughts.
1. If you use premier color, which is the only way to see sRGB correctly, you see the colors banding, but not everywhere. for example in Lightroom and photoshop works well, but in chrome, in moview or in your background you see the banding.
2. If you dont use premier color you see oversaturated colors and if you calibrate your screen you also see good colors in Adobe programs and oversaturated in all the other apps.
My conclution is that something happened with DELL BIOS update between the Intel graphics and the monitor. I think that the system doesn't listen to work the ICC profile in every situation.
If you read carefully what im saying, you will see that every program which use the nVidia graphics (like Adobe programs) the colors looks good.
Let me know guys if you agree with what im saying...